Alcohol versus mechanical epithelial debridement: effect on underlying cornea before excimer laser surgery.

PURPOSE: To determine the effects of 70% isopropyl alcohol used for corneal debridement on surface smoothness, stromal keratocytes, and ease of epithelial removal. SETTING: Cornea Research Laboratory, University of Rochester, and Excimer Laser Laboratory, Genesee Valley Eye Institute, Rochester, New York, USA. METHODS: Rabbit corneas were de-epithelialized mechanically or with 70% alcohol. The rabbits were split into groups and evaluated immediately or after a 50 microns deep excimer laser phototherapeutic keratectomy. All tissue was evaluated and compared in terms of surface smoothness parameters, loss of keratocytes, and inflammatory response to de-epithelialization. RESULTS: Computerized laser interferometric microscopy showed no between-group difference in the surface smoothness parameters. There was a marked absence of keratocytes in the superficial 25% of the corneal stroma. The loss of keratocytes was significantly higher (P < .001) in corneas treated with isopropyl alcohol. The inflammatory response 24 hours after epithelial removal was significantly higher (P < .001) in the corneas treated with alcohol. CONCLUSION: The use of 70% isopropyl alcohol applied for 2 minutes for epithelial removal did not enhance the quality of the subsequent excimer laser procedure. In contrast, isopropyl alcohol increased the inflammatory response, and it may have damaging effects on keratocytes. We would not advocate the use of 70% isopropyl alcohol as administered in our study to remove corneal epithelium before excimer laser surgery.

Clinical effect of blowing nitrogen gas across the cornea during photorefractive keratectomy.

OBJECTIVE: We evaluated the clinical effects of blowing nitrogen gas over the cornea during photorefractive keratectomy. METHODS: We retrospectively compared clinical outcomes of 32 patients (37 eyes), divided into two groups who had photorefractive keratectomy with nitrogen gas blowing across the cornea (n = 19) and without nitrogen gas (n = 18). All photorefractive keratectomies were performed between April 1991 and August 1992. Ablation zone diameters were 5.0 or 5.5 mm. The average attempted correction was -3.47 +/- 1.76 diopters (D) in the nitrogen gas group, and -3.48 +/- 1.25 D in the non-nitrogen gas group. RESULTS: The nitrogen gas group achieved more accurate corrections than the non-nitrogen gas group, but had a significantly greater amount of corneal haze at all postoperative examinations. Corneal haze was most evident at 1 month and gradually diminished therafter in both groups. At 6 months, videokeratography revealed a central island in 2 eyes (11.1%) of the non-nitrogen gas group. Because of undercorrection (2 eyes) or central island (1 eye), 3 out of 18 eyes in the non-nitrogen gas group were reablated 6 months later. CONCLUSIONS: The non-nitrogen gas group had more undercorrections and a higher frequency rate of central steep islands, but nitrogen gas blowing caused a greater amount of corneal haze.

Posterior capsule polishing with the neodymium:YLF picosecond laser: model eye study.

PURPOSE: To determine the ability and threshold energy of the neodymium:yttrium-lithium-fluoride (Nd:YLF) picosecond laser to achieve micron-level polishing of a latex posterior capsule facsimile (PCF) as an alternative to laser capsulotomy to treat posterior capsule opacification. SETTING: University of Rochester Medical Center, Rochester, New York, USA. METHODS: A solid-state, mode-locked Nd:YLF picosecond laser was used to polish a latex PCF in contact with a poly(methyl methacrylate) intraocular lens (IOL) in an experimental model eye. Eight study groups were treated at different energy levels ranging from 5 to 15 microJ. All treatments were done at least three times in different latex capsules and lenses. An atomic force microscope was used to measure IOL damage and an interferometric surface analysis microscope to assess the polishing effect on the PCF. The IOLs were further subjected to a scatter analysis to assess the optical significance of the damage produced. RESULTS: The latex PCF revealed a polishing effect with all energy settings used. The IOLs were damaged with all energy settings but 5 microJ. Energy settings higher than 5 microJ caused significantly more polishing effect to the latex and damage to the lenses. At the 10 microJ energy level, a single parameter with no depth produced a relative polishing depth of 3.01 microns +/- 0.10 (root mean square +/- SD). At this energy, the damage to the IOLs was 188 +/- 20.52 nm, and it was associated with typical craters over the surface at regular intervals that corresponded to each individual laser pulse. CONCLUSION: This model documented the feasibility of achieving micron-level precision in excising material with the picosecond laser and showed that posterior capsule polishing should be feasible and safe in human eyes.

Corneal incisions utilizing the 1,053-nm picosecond Nd:YLF ophthalmic laser.

We evaluated the precision and predictability of a 1,053-nm picosecond Nd:YLF ophthalmic laser with various combinations of computer-controlled parameters. We utilized epithelium-free corneal-sclera preparations from NZW rabbits, and the 1,053-nm Nd:YLF laser (Intelligent Surgical Lasers, San Diego, CA, U.S.A.). X-line and line patterns were utilized to make linear corneal incisions. Three parameters (layer size, crossing width, and energy level) were evaluated. One parameter was changed for a total of 120 combinations of computer-controlled parameters. Three incisions were performed for each combination. Although the intended depths of the incisions were constant (300 mu m), the actual depths of the incisions varied with the change of parameters. Increasing layer size decreased the depth of incisions, and increasing crossing width or energy level increased the depth of incisions. Only three of 120 combinations of parameters achieved depths near 300 mu m. Within the same combination of parameters, the depth of the corneal incisions varied. Debris of ablated stromal tissue was observed at the border and partially occupying the incision. Most of the incisions were "funnel"-shaped with the distal treatment zone having a "zigzag" or irregular border. Further improvements are necessary to use this laser system for corneal transverse incisions.

Effect of corticosteroids on rabbits corneal keratocytes after photorefractive keratectomy.

BACKGROUND: To determine the corticosteroid effect on the activity and repopulation of keratocytes after photorefractive keratectomy (PRK). METHODS: A 193-nm excimer laser (VISX Twenty/Twenty) created a central ablation depth of 22 microns (diameter:5 nm) on 22 corneas of 16 albino rabbits. Two ablated eyes were examined 6 hours following PRK. Twelve eyes received no postoperative corticosteroids and eight were treated with topical fluoromethalone for 3 months. Corneas were examined 1, 3, 6, and 12 months after PRK by immunofluorescence and transmission electron microscopy. RESULTS: Corticosteroids reduced haze (p=0.02), but all corneas (treated or untreated) cleared 6 months after PRK. Keratocytes were absent from the anterior 100 microns of the stroma 6 hours after PRK. However, the number and activity of keratocytes were significantly greater in this area in untreated corneas at 1 month and then gradually decreased. By 6 and 12 months, the number of keratocytes approached controls. Treated corneas had fewer keratocytes than either controls or untreated eyes (p<0.01) and by 3 months, a subepithelial acellular zone of 30 to 50 microns thickness appeared and persisted until at last 12 months after PRK. CONCLUSIONS: Corticosteroids have a transient effect in reducing haze and seem to inhibit keratocyte movement, leading to an acellular subepithelial region beneath the ablated area.

Effects of the picosecond neodymium:YLF laser on poly(methyl methacrylate) intraocular lenses during experimental posterior capsulotomy.

We evaluated the effect of the neodymium:YLF picosecond laser on intraocular lenses (IOLs) during experimental posterior capsulotomy and established the minimum damage threshold for lathe-cut poly(methyl methacrylate) (PMMA) IOLs. Single-piece, biconvex, lathe-cut PMMA lenses were placed in a model eye chamber against a latex membrane with a central area of lens-capsule touch. Energy levels from 40 micro J to 360 microJ pulse (0.4 mJ to 3.6 mJ) with a 0.5 mm line and a spot pattern were tested using different focal offsets. Threshold damage level was determined under the scanning electron microscope after observing the minimal energy level that did not cause damage to or pits in the IOLs. Lenses were then analyzed for size and type of damage. The 0.5 mm line pattern at 160 microJ using 350 microns offset was safe and effective for posterior capsulotomy in vitro. spot pattern caused IOL damage in the form of small pits at much lower energy levels of 80 microJ using 400 microns offset than the line pattern.

Cognitive styles and personality characteristics strongly influence the decision to have photorefractive keratectomy.

BACKGROUND: A substantial number of patients who elect to undergo photorefractive keratectomy do so without the motivation of occupational uncorrected vision requirements. We hypothesized that information processing preferences for the auditory (versus visual) modality in a global, associative (versus detailed, sensory-oriented) style with adaptability and risk-taking (versus predictability) personality characteristics would predominate in patients electing photorefractive keratectomy. METHOD: Seventy-three prospective photorefractive keratectomy patients attended informational sessions. Sixteen occupationally driven patients and one refusal were excluded from the analysis. The 27 patients electing to proceed with surgery were compared with the 29 declining surgery. Personality characteristics and cognitive styles were determined by the Myers-Briggs Type Indicator: Abbreviated Version and the Modality Strengths Indicator. RESULTS: Subjects electing surgery showed significantly greater preferences for processing information in the auditory modality and in a global, associative style, with adaptability and risk-taking personality characteristics. Combining the attributes statistically differentiated the two groups. CONCLUSIONS: Specific cognitive styles and personality characteristics strongly influence the choice to pursue photorefractive keratectomy when that choice is not occupationally driven.

Excimer laser photorefractive keratectomy after radial keratotomy.

BACKGROUND: Correction of residual myopia after radial keratotomy may be attempted with repeated keratotomy surgery, but predictability can be less than satisfactory. Excimer laser photorefractive keratectomy (PRK) provides an alternative approach to improving the refractive result in these patients. METHODS: Twenty-five eyes of 20 patients at five clinical locations underwent PRK for residual myopia after radial keratotomy. The number of incisions ranged from 4 to more than 16. Clear zones ranged from 3 mm to 4 mm. Best corrected visual acuity was 20/20 or better in 16 of the 25 eyes, with a range from 20/12 to 20/80. Uncorrected visual acuity was 20/200 or worse in 15 of the 25 eyes, with a range from 20/25 to finger counting. The interval between radial keratotomy and PRK averaged 33.5 months, with a range from 5 to 96 months. Nineteen eyes had 6 months or more of follow up; 15 had 12 months or more. RESULTS: Corneal haze was maximal 1 month after surgery (mean +/- SE, 0.65 +/- 0.09), and declined to 0.35 +/- 0.16 at 12 months. Twelve months after PRK, mean keratometric readings were 40.19 +/- 0.81 diopters (D) and mean spherical equivalent refraction was -1.42 +/- 0.47 D. Nine (60%) of the 15 eyes with 12 months follow up were within 1 D of emmetropia and 12 (80%) were within 2 D. Eight (53%) of the 15 eyes had uncorrected visual acuities of 20/40 or better. Spectacle-corrected visual acuity in the eyes with 12 months follow up improved in 4, did not change in 4, and worsened in 6. CONCLUSIONS: The results of PRK are less predictable in eyes that have previously undergone radial keratotomy, and these eyes respond with more haze after PRK than normal eyes.

Evaluation of tissue adhesives in closure of scleral tunnel incisions.

Using a biomechanical wound strength model, we compared the efficacy of cyanoacrylate and fibrin glues used to close scleral tunnel incisions. Scleral tunnel incisions were made in four groups of rabbits: (1) traditional self-sealing incision, (2) modified non-self-sealing incision, (3) method 2, closed with cyanoacrylate glue, or (4) method 2, closed with fibrin glue. Overall, Groups 1 and 4 showed the least clinical reaction, the slightest decrease in intraocular pressure (which recovered to baseline by day 7), and the most significant recovery of postoperative astigmatism. Initially, the bursting pressure in Groups 1 and 3 was statistically the highest (P < .005). By day 3, wound strengths in Groups 1 and 4 were comparable. Bursting pressure decreased in Groups 2 and 3 by day 7. Our results indicate that clinical responses, intraocular pressure, induced astigmatism, and ultimately wound strength were comparable in fibrin-glue-closed scleral pocket and sutureless self-sealing cataract incisions. Although cyanoacrylate glue cures immediately and initially demonstrates a strong adhesive quality, it causes a severe inflammatory response that inhibits subsequent collagen remodeling. Fibrin tissue adhesives may have an application as adjunctive means of closing scleral tunnel incisions.

[Correlation between corneal sensitivity and nerve regeneration following excimer laser ablation].

To compare the recovery of corneal sensitivity and corneal regeneration following excimer laser and manual epithelial debridement, the corneal epithelium of the right eye of New Zealand white rabbits (n = 21) was manually debrided and the left eye was ablated with the excimer laser (47 microns depth, 5 Hz, and 160 mJ/cm2). We observed the wound healing rate and corneal sensitivity. The relative density of innervation on the intraepithelial layer was measured using gold chloride staining or right microscopic examination for 30 weeks. In the laser-ablated cornea sensitivity rapidly increased to a normal level by day 5, and then it continued to increase gradually and reached a maximum at day 42. Thereafter it remained elevated to 126 days and returned to normal at 210 days. There were significant differences in the recovery of sensitivity following excimer ablation and manual epithelial removal. The relative density of innervation on the intraepithelial layer after excimer ablation was significantly higher than manual debridement at day 35. We observed a correlation between increased sensitivity levels and increased nerve density. This result suggests that for photorefractive keratectomy or phototherapeutic keratectomy, manual debridement of the corneal epithelium should be performed before stromal excimer ablation.

Topical diclofenac following excimer laser: effect on corneal sensitivity and wound healing in rabbits.

BACKGROUND: Diclofenac is a nonsteroidal antiinflammatory drug (NSAID) that is widely used systemically and topically. We studied the effect of diclofenac on corneal reepithelialization and corneal sensitivity after excimer laser treatment in rabbits. METHODS: Twelve New Zealand white rabbits were divided into four groups (A, B, C, and D). Groups A and B received diclofenac four times and eight times daily, respectively, following a central 5-millimeter epithelial debridement. Groups C (control) and D (diclofenac four times daily) underwent excimer laser ablation (30-micrometer depth) following manual debridement. Wound healing was compared between groups A and B and groups C and D. Sensitivity was recorded preoperatively and postoperatively 1 to 5 and 14 days in groups C and D until normal values were reestablished. RESULTS: Total time for corneal wound healing and epithelial migration rates was not delayed in any group receiving diclofenac (A, B, and D). Sensitivity after laser ablation reached a minimum of 15% to 20% in both groups C and D by day 2 and returned to normal (100%) by day 8. The decrease in sensitivity between group C, the controls, and group D, receiving diclofenac four times daily, was not statistically significant. CONCLUSIONS: Diclofenac can be used up to eight times daily in the rabbit without causing changes in corneal wound healing or epithelial migration rate. There was no significant, long-term reduction of sensitivity, and recovery was not affected by diclofenac.

Corneal sensation following excimer laser photorefractive keratectomy in humans.

BACKGROUND: For the correction of myopia, small amounts of corneal tissue--including corneal nerves--are removed, resulting in flattening of the central cornea. METHODS: We studied the changes in corneal sensation in five regions of the cornea following photorefractive keratectomy at varying depths. We examined and compared the recovery of sensation in 17 sighted myopic eyes, with preoperative refractive ranges from -1.00 to -7.25 D. Eyes were divided into shallow (0 to 30 microns) or deep (31 to 70 microns) ablation groups depending on the attempted laser correction. Corneal sensation was measured in the central ablated area and the temporal, inferior, nasal, and superior unablated regions preoperatively and at 1, 3, and 6 months postoperatively. RESULTS: Central and inferior sensation were significantly reduced in the deep ablations at 1 month and continued in the central cornea 6 months postoperatively. There were no overall differences in the sensations in the unablated nasal, temporal, and superior regions between either group or over time. There was a significant second order trend (p = .034) in these three regions, indicating a sharper increase in sensation from baseline in the deeper group at 1 month than the gradual upward trend of the shallow group. CONCLUSIONS: Corneal sensation of both the central ablated area and the unablated peripheral cornea is decreased after deep anterior stromal excimer laser ablations and does not recover within 1 month. Although the deeper group showed isolated areas in the periphery of significant second order trends in sensation, the overall trends were not large, indicating no significant anesthetic effect. Fluctuations in sensation can be detected in the five regions even 6 months after excimer laser keratectomy. The clinical importance of these data remain to be defined.

Corneal sensitivity and nerve regeneration after excimer laser ablation.

We studied the recovery of corneal sensitivity and corneal regeneration after excimer laser and manual epithelial debridement. The corneal epithelia of right eyes of New Zealand white rabbits (n = 21) were manually debrided and the corneal epithelia of the left eyes were ablated with the excimer laser (47 mm depth, 5 Hz, and 160 mJ/cm2). The relative density of innervation on the intraepithelial layer was measured using gold chloride staining and light microscopy. Wound healing and corneal sensitivity also were observed. Laser-ablated corneal sensitivity increased rapidly to a normal level by day 5, then increased gradually and reached a maximum at day 42. It remained elevated until 126 days, then returned to normal at 210 days. There were significant differences in the recovery of sensitivity after excimer ablation and manual epithelial removal. At day 35, relative density of innervation in the intraepithelial layer treated with excimer laser ablation was significantly higher than that treated with manual debridement. We observed a correlation between increased sensitivity and increased nerve density after excimer ablation. Compared with manual debridement, laser treatment resulted in an increase in networks of axons with terminal endings. This may not be the only factor correlating directly with hypersensitivity after corneal debridement, but it may indicate a quicker recovery route by using a presurgical manual debridement technique.

Surface quality of excimer laser corneal ablation with different frequencies.

To test the effects of different frequencies of a 193-nm excimer laser on the surface smoothness of the ablated materials and the damage to the adjacent structure, four different frequencies (5, 10, 15, and 20 Hz) of a 193-nm excimer laser were used to perform ablations on 20 rabbit corneas and four polymethylmethacrylate blocks at a fluence of 160 mJ/cm2. Each frequency was tested five times on five corneas. The ablated materials were processed and examined with scanning electron microscopy (SEM) and light and transmission electron microscopy (TEM) and a Zygo interference microscope, which quantitatively evaluates the surface smoothness. The results from the Zygo microscope show that there is no statistically significant difference in surface smoothness between any two different frequencies. The SEM reveals similar regularity and uniformity on the ablated surfaces, with no relationship between the laser frequencies and the amount of surface deposits. The TEM demonstrates no correlation between the various frequencies and the thickness of the superficial pseudomembrane and the amount of collateral damage in the adjacent stroma. It appears that the higher frequencies are comparable to the lower one (5 Hz) as to ablation quality, with the benefit of curtailing surgical time and decreasing the chances of eye movement.

Intraocular lens dislocation in the bag.

We report a case in which an intraocular lens dislocated entirely within the capsular bag. The patient was myopic with a large anterior segment. A standard 5 mm x 6 mm phaco profile intraocular lens was found to be completely dislocated on the fifth postoperative day. The dislocated lens was replaced with another posterior chamber intraocular lens sutured at the ciliary sulcus.

Excimer laser keratectomy after radial keratotomy.

Radial keratotomy to treat myopia has been characterized by a lack of predictability. Until recently, patients with undercorrected myopia who were unsatisfied with their visual outcome could only be offered secondary augmentation procedures, which were equally unpredictable. We performed excimer laser keratectomy in six eyes of five patients whose myopia was undercorrected after radial keratotomy. The average residual spherical equivalent refractive error after radial keratotomy was -2.40 diopters, and this was reduced to -0.48 diopters after laser treatment. Final uncorrected visual acuity ranged from 20/80 to 20/20, and visual acuity was corrected to within one line of the preoperative best-corrected value in all patients. Epithelialization of all eyes occurred within four to six days. There were no incidences of corneal neovascularization, including no vascularization of the radial keratotomy incisions. Our findings suggest excimer phototherapeutic keratectomy offers a safe and more controlled method of augmenting undercorrected myopia after radial keratotomy.

Endogenous endophthalmitis caused by Escherichia coli.

Endophthalmitis is a rare complication of Escherichia coli-induced septicemia. Nine cases of endogenous endophthalmitis caused by E. coli have been reported previously, all except one in patients with diabetes. The most common primary site of infection is the urinary tract. The course of illness is rapidly progressive with a poor visual prognosis. Concurrent systemic morbidity, including body abscesses and endocarditis, is high. We report an additional case of endogenous endophthalmitis from E. coli in a diabetic woman. Enucleation was required despite aggressive topical and systemic treatment. The pertinent literature is reviewed.